This invention relates to a fuel-air ratio control apparatus for overriding an engine governor means to preclude an increase of fuel to the engine during a reduction of air pressure in the engine intake manifold. Engines equipped with superchargers smoke badly under lug. Lug is encountered when resistance or load on the engine is increased to the extent that engine speed is reduced below that which is indicated by the governor setting. Under these conditions, the engine governor attempts to regain the engine speed indicated by the governor setting by automatically advancing the engine fuel rack to supply more fuel. However, due to the reduction in supercharger speed caused by the reduced engine speed, insufficient air is supplied to the engine to support complete combustion of the additional fuel being injected. The patent to Crews, et al, U.S. Pat. No. 3,795,233, of common assignment herewith teaches a fuel-air control apparatus for resolving the problems as described above. However, it was found that even with this control apparatus, excessive amounts of secondary exhaust plumes were still being generated during engine lug.